Repairing bricked Samsung GT-P6810 Galaxy Tab 7.7 WiFi 16GB is easy with RIFF Box.
Samsung P6810 is based on the Exynos Processor (Cortex-A9 Dual-Core). JTAG pads are very small; professional experience in soldering is required to connect wires to the JTAG interface.
Note, one simple way to connect over JTAG – connect USB cable to PC and insert battery. In this case phone is automatically powered on.

To resurrect Samsung P6810:

Solder JTAG cable to Samsung P6810 JTAG pads;

Connect USB cable to phone and PC;

Insert battery;

Make sure Samsung P6810 is selected in the list of models;

Make sure a fixed TCK frequency is selected;

Click Resurrect button;

Wait till software signals a successful operation completion;

Disconnect USB cable, de-solder JTAG wires;

Now phone is in bootable condition, that is, even if it does not start up normally, you can flash it using original Samsung downloader software to restore it to the working state.